Medical image processing apparatus and medical image processing method which are for medical navigation device

ABSTRACT

The present invention relates to a medical image processing apparatus and a medical image processing method for a medical navigation device, and more particularly, to an apparatus and method for processing an image provided when using the medical navigation device. To this end, the present invention provides a medical image processing apparatus for a medical navigation device, including: a position tracking unit configured to obtain position information of the medical navigation device within an object; a memory configured to store medical image data generated based on a medical image of the object; and a processor configured to set a region of interest (ROI) based on position information of the medical navigation device in reference to the medical image data, and generate partial medical image data corresponding to the ROI, and a medical image processing method using the same.

TECHNICAL FIELD

The present invention relates to a medical image processing apparatusand a medical image processing method for a medical navigation device,and more particularly, to an apparatus and method for processing animage provided when using the medical navigation device.

BACKGROUND ART

A minimally invasive surgery that minimizes the incision site of thepatient during surgery is widely used. The minimally invasive surgeryhas an advantage of minimizing the incision and thus minimizing bloodloss and recovery time, but restricts the doctor's field of view thushaving some risk factors such as meninx damage and eye damage in somesurgeries. As a tool for overcoming the disadvantages of minimallyinvasive surgery in which the doctor's field of view of is restricted, amedical navigation device (or surgical navigation device) is used. Themedical navigation device tracks in real time the position of theinstrument in the surgical site in reference to a previously obtainedmedical image of the patient. In addition, such a medical navigationdevice may be used in combination with an endoscope.

An optical or electromagnetic position tracking devices may be used forreal-time position tracking of the inserted surgical instrument in themedical navigation device. As an example for tracking the position ofthe surgical instrument, an optical position tracking device includingan infrared emitting device and a passive image sensor may be used. Theoptical position tracking device emits reference light through theinfrared emitting device and collects the image reflected by pluralmarkers through the image sensor. The position tracking apparatus mayobtain position information of the surgical instrument based on thepositions of the markers. Meanwhile, as another example for tracking theposition of the surgical instrument, an electromagnetic positiontracking device including a magnetic field generator and a conductivemetal object may be used. The electromagnetic position tracking devicemay obtain the position information of the surgical instrument bymeasuring the eddy current occurs in the conductive metal object in themagnetic field generated by the magnetic field generator. In order toaccurately indicate the positional relationship between the surgicalinstrument and the body part in the position tracking device, aregistration process may be required that defines the initial positionalrelationship between the medical data for the patient's body part andthe surgical instrument.

FIG. 1 illustrates an embodiment of an output image of a medicalnavigation device. The medical navigation device may display at leastone of horizontal, sagittal, and coronal images of a body part. Theoperator (or doctor) interprets each image to determine thethree-dimensional position of the surgical instrument, and to identifyadjacent risk factors. However, these cross-sectional images are notintuitive representation of the position of the surgical instrument insurgical site. Therefore, in order to identify the exact position of thesurgical instrument with cross-sectional images, the operator may need alot of time as well as a skill. In addition, when the time of looking atthe monitor of the medical navigation device to determine the positionof the surgical instrument is prolonged, the overall surgery timebecomes long, which may increase the fatigue of both the operator andthe patient.

DISCLOSURE Technical Problem

The present invention has an object to provide a medical imageprocessing method for helping the operator to intuitively identifyinformation on surgical site and adjacent elements (e.g. organs) in apatient's body.

In addition, the present invention has an object to effectively renderthe medical image of the patient taken in advance and the intraoperativeimage in surgical site.

In addition, the present invention has an object to provide a medicalnavigation device that is easy to identify the patient's anatomicalstructure.

Technical Solution

In order to solve the above problems, the present invention provides amedical image processing apparatus and a medical image processing methodas follows.

First, an exemplary embodiment of the present invention provides amedical image processing apparatus using an augmented reality,including: an endoscopic image obtaining unit which obtains anendoscopic image of an object; a memory which stores medical image datagenerated based on a medical image of the object; and a processor whichobtains position and direction information of the endoscope in referenceto the medical image data, determines a target area to be displayed inaugmented reality among the medical image data based on the obtainedposition and direction information, and renders partial medical imagedata corresponding to the target area as an augmented reality image onthe endoscopic image.

In addition, an exemplary embodiment of the present invention provides amedical image processing method using an augmented reality, including:obtaining an endoscopic image of an object; obtaining position anddirection information of the endoscope in reference to medical imagedata of the object, wherein the medical image data of the object isgenerated based on a medical image of the object; determining a targetarea to be displayed in augmented reality among the medical image databased on the obtained position and direction information; and renderingpartial medical image data corresponding to the target area as anaugmented reality image on the endoscopic image.

According to an embodiment, the medical image data may include dataobtained by synthesizing the medical image of the object and userdefined auxiliary data and performing volume rendering on thesynthesized data.

In this case, the auxiliary data may be represented as a voxel having avalue outside a pre-defined Hounsfield Unit (HU) range.

In addition, the range outside pre-defined HU range may include a firstHU range exceeding a first threshold and a second HU range below asecond threshold, and a value of the first HU range and a value of thesecond HU range may represent different types of auxiliary data.

According to an embodiment, the pre-defined HU range may reach from−1000 HU to +1000 HU.

According to another embodiment of the present invention, the processormay generate a first normal map using the endoscopic image, and obtainthe position and direction information of the endoscope in reference tothe medical image data based on a result of determining a similaritybetween the first normal map with a plurality of second normal mapsobtained from the medical image data.

In this case, the processor may compare the first normal map with secondnormal maps within a preset range from a position and a direction of theendoscope at a previous time point.

According to an embodiment, the first normal map may be obtained basedon reflection information of structured light with respect to a searcharea of the object.

In addition, the second normal map may be obtained from the medicalimage data based on position and direction information of a virtualendoscope for the object.

In addition, the direction information of the virtual endoscope may bedetermined based on a straight line connecting a start point (or aprevious position) of a path of the virtual endoscope and a currentposition of the virtual endoscope.

Next, another exemplary embodiment of the present invention provides amedical image processing apparatus for a medical navigation device,including: a position tracking unit which obtains position informationof the medical navigation device within an object; a memory which storesmedical image data generated based on a medical image of the object; anda processor which sets a region of interest (ROI) based on positioninformation of the medical navigation device in reference to the medicalimage data, and generates partial medical image data corresponding tothe ROI.

In addition, another exemplary embodiment of the present inventionprovides a medical image processing method for a medical navigationdevice, including: obtaining position information of the medicalnavigation device within an object; storing medical image data generatedbased on a medical image of the object; setting a region of interest(ROI) based on position information of the medical navigation device inreference to the medical image data; and generating partial medicalimage data corresponding to the ROI.

In this case, the ROI may be set based on an area within a presetdistance from a position of the medical navigation device in referenceto at least one of a horizontal plane, a sagittal plane, and a coronalplane of the medical image data.

In addition, the preset distance in reference to each of the horizontalplane, the sagittal plane, and the coronal plane may be determined by auser input.

According to an embodiment, the partial medical image data may begenerated by rendering voxels having a value within a pre-definedHounsfield Unit (HU) range in the ROI.

In addition, the pre-defined HU range may be determined based on a CTvalue of a specific tissue of the object.

In addition, the specific tissue may be arbitrarily determined by auser.

According to a further embodiment of the present invention, the partialmedical image data may be generated by rendering voxels in the ROI witha light from a virtual light source at a predetermined point based on aposition of the medical navigation device.

In this case, each pixel value I(S₀,S_(n)) of the partial medical imagedata may be determined based on the following equation.

I(S₀, S_(n)) = ∫_(S₀)^(S_(n)){I_(λ)(x)e^(−∫_(S₀)^(x)τ(t)dt) + K_(ref) ⋅ L ⋅ e^(−∫_(P₀)^(x)τ(t)dt)}dx

Herein, S₀ is a first voxel sampled by ray casting, S_(n) is a lastvoxel sampled by ray casting, I_(λ)(x) is a value of voxel x, τ(t) is anattenuation coefficient of voxel t, K_(ref) is a reflection coefficient,P₀ is a position of the virtual light source, L is a brightness value ofthe virtual light source at P₀.

In this case, the K_(ref) may be determined based on the followingequation.K _(ref)=max(G(x)*V _(p0→x),0)

Herein, G (x) is a gradient vector at voxel x, and V_(p0→x) is adirection vector from a position P₀ of the virtual light source to voxelx.

In addition, the medical image data may be set of voxels generated usingthe medical image of the object, and the partial medical image data isvolume rendering data obtained by applying ray casting on voxels in theROI.

Advantageous Effects

According to an embodiment of the present invention, the medical imageand the surgical site image of the patient may be effectively renderedto provide convenience of surgery and medical diagnosis.

In addition, according to an embodiment of the present invention, it ispossible to minimize the amount of computation required to renderadditional data included in the medical image.

In addition, according to an embodiment of the present invention, theoperator can easily identify the anatomical structure of the patientthereby improving the convenience and concentration on the surgery.

DESCRIPTION OF DRAWINGS

FIG. 1 illustrates an embodiment of an output image of a medicalnavigation device.

FIG. 2 is a block diagram of a medical image processing apparatusaccording to an embodiment of the present invention.

FIG. 3 is a more detailed block diagram of a processor of the medicalimage processing apparatus according to an embodiment of the presentinvention.

FIG. 4 is a block diagram of an endoscope tracking unit according to anembodiment of the present invention.

FIG. 5 illustrates an endoscopic image and a normal map generated usingthe same.

FIG. 6 illustrates an embodiment that medical image data is provided asan input of augmented reality image of endoscopic image.

FIGS. 7 and 8 illustrate a volume rendering technique according to anembodiment of the present invention.

FIG. 9 is a block diagram of a medical image data generator according toan embodiment of the present invention.

FIG. 10 is a block diagram of a medical image processing apparatusaccording to another exemplary embodiment of the present invention.

FIG. 11 is a more detailed block diagram of a processor of the medicalimage processing apparatus according to another embodiment of thepresent invention.

FIG. 12 illustrates an example of defining region of interest withrespect to an object.

FIG. 13 illustrates partial medical image data corresponding to theregion of interest defined in an embodiment of FIG. 12.

FIG. 14 illustrates an embodiment of user interface for defining aregion of interest with respect to an object.

FIGS. 15 and 16 illustrate partial medical image data corresponding tovarious regions of interest.

FIG. 17 illustrates a method of generating partial medical image dataaccording to an additional embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

In the specification, up to date general terms are used consideringfunctions in the present invention, but they may be changed depending onan intention of those skilled in the art, customs, and emergence of newtechnology. Further, in a specific case, there is a term arbitrarilyselected by an applicant and in that case, a meaning thereof will bedescribed in a corresponding description part of the invention.Accordingly, it should be revealed that a term used in the specificationshould be understood on not just a name of the term but a substantialmeaning of the term and contents throughout the specification.

Throughout this specification and the claims that follow, when it isdescribed that an element is “coupled” to another element, the elementmay be “directly coupled” to the other element or “electrically coupled”to the other element through a third element. Further, unless explicitlydescribed to the contrary, the word “comprise” and variations such as“comprises” or “comprising”, will be understood to imply the inclusionof stated elements but not the exclusion of any other elements.Moreover, limitations such as “or more” or “or less” based on a specificthreshold may be appropriately substituted with “more than” or “lessthan”, respectively.

Hereinafter, a medical image processing apparatus and a medical imageprocessing method according to an exemplary embodiment of the presentinvention will be described with reference to the drawings. The imageprocessing apparatus and the image processing method according to theembodiment of the present invention may be applied to a medical image ofan object including a human body and an animal body. The medical imageincludes an X-ray image, a computed tomography (CT) image, a positronemission tomography (PET) image, an ultrasound image, and a magneticresonance imaging (MRI), but the present invention is not limitedthereto. In addition, in the present description, the term medical imagedata is used as a term in a broad sense including not only the medicalimage itself but also various types of data generated by rendering themedical image. According to an embodiment, the medical image data mayrefer to data obtained by performing volume rendering on the medicalimage. In addition, the medical image data may refer to athree-dimensional data set composed of a group of two-dimensionalmedical images. The value on a regular grid in the three-dimensionaldata set configured as described above is called a voxel. The medicalimage processing apparatus and the medical image processing methodaccording to an embodiment of the present invention may generate orprocess an image provided by an endoscope and/or a medical navigationdevice.

FIG. 2 is a block diagram of the medical image processing apparatus 10according to an embodiment of the present invention. As illustrated, themedical image processing apparatus 10 according to an embodiment of thepresent invention may include a processor 11, a communication unit 12,an input unit 13, a memory 14, an endoscopic image obtaining unit 15,and a display output unit 16.

First, the communication unit 12 includes a wired/wireless communicationmodule of various protocols for communicating with an external device.The input unit 13 includes various types of interfaces for receiving auser input for the medical image processing apparatus 10. According toan embodiment, the input unit 13 may include a keyboard, a mouse, acamera, a microphone, a pointer, a USB, a connection port with anexternal device, and the like, but the present invention is not limitedthereto. The medical image processing apparatus may obtain a medicalimage of the object through the communication unit 12 and/or the inputunit 13 in advance. The memory 14 stores a control program used in themedical image processing apparatus 10 and various data related thereto.For example, the memory 14 may store a previously obtained medical imageof an object. In addition, the memory 14 may store medical image datagenerated by rendering the medical image of the object.

The endoscopic image obtaining unit 15 obtains an endoscopic image of asearch area of an object captured by the endoscope 50. The endoscopicimage obtaining unit 15 may be connected with the endoscope 50 by wireor wireless to receive an image from the endoscope 50.

The display output unit 16 outputs an image generated according to anembodiment of the present invention. That is, the display output unit 16may output an augmented reality image together with the endoscopic imageof the object as described below. In this case, the augmented realityimage may include partial medical image data corresponding to theendoscopic image. The image output by the display output unit 16 may bedisplayed by the monitor 60 connected to the medical image processingapparatus 10.

The processor 11 of the present invention may execute various commandsand programs and process data in the medical image processing apparatus10. In addition, the processor 11 may control each unit of the precedingmedical image processing apparatus 10 and control data transmission andreception between the units.

The medical image processing apparatus 10 illustrated in FIG. 2 is ablock diagram according to an exemplary embodiment of the presentinvention, in which the separately displayed blocks logicallydistinguish elements of the apparatus. Therefore, the preceding elementsof the medical image processing apparatus 10 may be mounted on one chipor on plural chips according to the design of the correspondingapparatus. In addition, some of the components of the medical imageprocessing apparatus 10 illustrated in FIG. 2 may be omitted, andadditional components may be included in the medical image processingapparatus 10.

FIG. 3 is a more detailed block diagram of the processor 11 of themedical image processing apparatus 10 according to an embodiment of thepresent invention. As illustrated, the processor 11 of the medical imageprocessing apparatus 10 according to an embodiment of the presentinvention may include an endoscope tracking unit 110, a medical imagedata generator 120, a partial medical image data extractor 130 and anaugmented reality data generator 140.

The endoscope tracking unit 110 obtains position and directioninformation of the endoscope 50 that provides an endoscopic image to themedical image processing 10. More specifically, the endoscope trackingunit 110 obtains the position and direction information of the endoscope50 (e.g., position and direction information of the endoscope camera)based on a medical image data coordinate system of the object. Accordingto an embodiment of the present invention, the endoscope tracking unit110 may track the position and direction of the endoscope 50 byanalyzing the endoscopic image obtained through the endoscopic imageobtaining unit 15. Specific embodiments thereof will be described later.Meanwhile, according to another embodiment of the present invention, theendoscope tracking unit 110 may include a separate endoscope trackingdevice to track the position and direction of the endoscope 50. When a 6degree of freedom (DOF) tracking device is coupled to the endoscope 50,the endoscope tracking unit 110 may obtain the position and directioninformation of the endoscope 50 from the tracking device. When theregistration process is performed on the position and directioninformation obtained from the tracking device, the position anddirection information of the endoscope 50 in reference to the medicalimage data coordinate system may be obtained.

Next, the medical image data generator 120 renders a medical image ofthe object to generate medical image data. As described above, themedical image includes at least one of an X-ray image, a CT image, a PETimage, an ultrasound image, and an MRI. According to an embodiment, themedical image data generator 120 may generate medical image data byperforming volume rendering on the medical image of the object. Inaddition, the medical image data generator 120 may generate medicalimage data by synthesizing the medical image of the object and the userdefined auxiliary data and performing volume rendering on thesynthesized data. Specific embodiments thereof will be described later.

Next, the partial medical image extractor 130 extracts the partialmedical image data to be displayed in augmented reality among themedical image data based on the computed position and directioninformation of the endoscope 50. More specifically, the partial medicalimage extractor 130 determines a target area (i.e., field of view) to bedisplayed in augmented reality among the medical image data based on theposition and direction information of the endoscope 50. According to anembodiment of the present invention, the target area may be determinedas a view frustum based on a specific focal length, a viewing angle, anda depth of the endoscope 50. Therefore, when the position and directioninformation of the endoscope 50 in reference to the medical image datacoordinate system is obtained by the endoscope tracking unit 110, atarget area to be represented in augmented reality within the medicalimage data may be determined. The partial medical image extractor 130extracts partial medical image data corresponding to the target areadetermined as described above.

Next, the augmented reality data generator 140 renders the augmentedreality image from the extracted partial medical image data. That is,the augmented reality data generator 140 may compose the partial medicalimage data with the endoscopic image and provide the partial medicalimage data as an augmented reality image for the endoscopic image.

FIG. 4 is a block diagram of the endoscope tracking unit 110 accordingto an embodiment of the present invention. In order to match theendoscopic image and the augmented reality image in a meaningful form,the following information is required.

-   -   The position P_(f)(X_(f), Y_(f), Z_(f)) of the endoscope 50 in        reference to the medical image data coordinate system    -   Direction vectors V_(view)(X_(v), Y_(v), Z_(v)), V_(up)(X_(u),        Y_(u), Z_(u)) and V_(right)(X_(r), Y_(r), Z_(r)) of the        endoscope 50 in reference to the medical image data coordinate        system    -   Field of view (FOV) of the endoscope 50    -   Focal length of the endoscope 50    -   Depth of field (DOF) of the endoscope 50

Among the information, the viewing angle, focal length, and depth offield follow the fixed specifications of the endoscope lens (i.e.,endoscope camera). Therefore, in order to determine a target area to berepresented in augmented reality within the medical image data, positionand direction information of the endoscope 50 should be obtained in realtime.

According to an embodiment of the present invention, the endoscopetracking unit 110 may track the position and direction of the endoscope50 via a separate endoscope tracking device. However, according toanother embodiment of the present invention, the endoscope tracking unit110 may track the position and direction of the endoscope 50 bycomparing the endoscopic image and the medical image data. Morespecifically, the endoscope tracking unit 110 tracks the position anddirection of the endoscope 50 by comparing a normal map based on anendoscopic image with plural candidate normal maps based on medicalimage data. The normal map maybe represented as two dimensionalprojection data of surface information of the search area.

Referring to FIG. 4, the endoscope tracking unit 110 may include a firstnormal map generator 112, a second normal map generator 114, and anormal map comparator 116. First, the first normal map generator 112obtains an endoscopic image and generates the first normal map M_(real)using the obtained endoscopic image. In general, an endoscopic imageincludes a spotlight type light source that is easy to find thedirection of the light. In addition, the inside of the human body, whichis observed by the endoscope, does not have a separate light source, andcontains a lot of reflective saliva on the surface. As a result, theendoscopic image may maximize effects of highlight and shade. Therefore,according to an exemplary embodiment of the present invention, the firstnormal map generator 112 may analyze the intensity of light in theobtained endoscopic image to generate the first normal map M_(real) inwhich the surface information of the three-dimensional search area isprojected to the two-dimensional form. The first normal map M_(real)generated by the first normal map generator 112 is transferred to thenormal map comparator 116.

FIG. 5 illustrates an endoscopic image and a normal map generated usingthe same. FIG. 5(a) shows an endoscopic image obtained from theendoscope 50, and FIG. 5(b) shows a normal map generated using theendoscopic image. As shown in FIG. 5(a), the endoscopic image mayclearly show highlights and shades on the curved surface. Accordingly,the medical image processing apparatus 10 of the present invention maygenerate a normal map as shown in FIG. 5(b) by analyzing the endoscopicimage.

According to a further embodiment of the present invention, anendoscopic image to which structured light or patterned light is appliedmay be used to generate a more accurate first normal map M_(real). Inthis case, the first normal map M_(real) is obtained based on thereflection information of the structured light or the patterned lightwith respect to the search area of the object.

Returning to FIG. 4, the second normal map generator 114 obtains pluralsecond normal maps M_(virtual) from the medical image data. The user maydetermine the searching path of the endoscope for the medical image datain advance and store the information. According to an embodiment of thepresent invention, the second normal map generator 114 may divide thepredetermined endo scope searching path by predetermined interval andgenerate a virtual endoscopic image corresponding to each divided point.The second normal map M_(virtual) is obtained by using the virtualendoscopic image. The second normal map M_(virtual) may be obtained frommedical image data based on the position and direction information ofthe virtual endoscope (e.g., position and direction information of thevirtual endoscope camera) with regard to the object. In this case, thedirection information of the virtual endoscope may be determined basedon a straight line connecting the start point (or a previous position)of the path of the virtual endoscope with the current position of thevirtual endoscope. However, even if the virtual endoscope has the sameposition and the direction vector V_(view), plural second normal mapsM_(virtual) are required in consideration of the rotation of the virtualendoscope in reference to the direction vector V_(view). Therefore,according to an embodiment of the present invention, plural secondnormal maps M_(virtual) may be generated according to predeterminedangular interval with respect to one point may be obtained. The secondnormal map M_(virtual) generated by the second normal map generator 114is transferred to the normal map comparator 116.

The normal map comparator 116 compares the first normal map M_(real)obtained from the endoscopic image with the plural second normal mapsM_(virtual) obtained from the medical image data to determinesimilarity. The position and direction information of the endoscope 50in reference to the medical image data may be obtained based on thesecond normal map M_(virtual) with highest similarity as a result of thesimilarity determination. According to a further embodiment of thepresent invention, in order to reduce the computing complexity of thesimilarity measure of the normal map, the normal map comparator 116 maypreferentially compare the first normal map M_(real) with the secondnormal maps M_(virtual) within a preset range from the position and thedirection of the endoscope 50 at a previous time point.

When the position and direction information of the endoscope 50 isobtained, the medical image processing apparatus 10 may extract partialmedical image data to be displayed in augmented reality as describedabove, and render the extracted partial medical image data as anaugmented reality image.

FIG. 6 illustrates an embodiment that medical image data is provided asan augmented reality image for an endoscopic image. More specifically,FIG. 6(a) shows an endoscopic image, FIG. 6(b) shows partial medicalimage data, and FIG. 6(c) shows that partial medical image data isprovided as an augmented reality image for the endoscopic image. Whenthe position and direction information of the endoscope 50 in referenceto the medical image data coordinate system is obtained according to thepreceding embodiment of the present invention, the partial medical imagedata and the endoscopic image may be efficiently matched. Accordingly,information about the surgical site and the adjacent elements of theobject may be intuitively identified by the operator.

Meanwhile, the medical image data to be represented in augmented realitymay include various types of data. As described above, the medical imagedata may be data obtained by performing volume rendering on a medicalimage such as an X-ray image, a CT image, a PET image, an ultrasoundimage, and an MRI. According to a further embodiment of the presentinvention, the medical image data may include an image of a target organ(e.g., brain, eye, lung, heart, etc.) represented in a mesh form aftersegmentation in a medical image of the object. In addition, the medicalimage data may further include user defined auxiliary data. Theauxiliary data includes planning information such as markers and pathsinserted into the medical image before the surgery represented as amesh. According to an embodiment of the present invention, the medicalimage processing apparatus 10 may perform volume rendering on theauxiliary data represented in the mesh form together with the medicalimage without performing surface rendering on it. More specifically, themedical image processing apparatus 10 may generate medical image datafor augmented reality by synthesizing the auxiliary data with themedical image and performing volume rendering on the synthesized data.

FIGS. 7 and 8 illustrate a volume rendering technique according to anembodiment of the present invention. The volume rendering is a techniquefor displaying two-dimensional projection images of three-dimensionalsample data set. The general three-dimensional data set may be composedof a group of two-dimensional tomographic images collected from thepreceding medical images. The images of the group may have a regularpattern and same number of pixels. The value on a regular grid in thethree-dimensional data set configured as described above is called avoxel.

FIG. 7 illustrates a ray-casting technique that may be used in volumerendering. The ray casting method is defined as that the voxelsconstituting the volume have the property of being translucent andemitting light by themselves. The ray casting method accumulates voxelvalues sampled along with each ray r₀, r₁, . . . , r₄ determinedaccording to the line of sight of the user (or the position anddirection of the camera) to obtain a rendering value (i.e., pixelvalue). In this case, the number of rays are determined according to theresolution of the resultant image. The color cube technique can be usedto properly render three-dimensional volume data according to the lineof sight of the user.

FIG. 8 illustrates a color cube used in volume rendering. As shown inFIG. 8, the color cube assigns black to the origin (0, 0, 0), assignswhite to the vertex (1, 1, 1) diagonally opposite to the origin, andincreases the intensity of the corresponding RGB value as the value ofeach coordinate increases within the cube. The RGB value for eachcoordinate is used as normalized texture sampling coordinate value.

In order to define the start point and the end point of each ray in thevolume rendering, front and the rear face of color cube images with thesame size (that is, the pixel size) may be generated. The value obtainedat the same position of each of the two generated images becomes thestart point and the end point of the ray corresponding to the position.When accumulating the values obtained by performing three-dimensionaltexture sampling of the medical image with a predetermined intervalalong with the ray from the start point to the end point, the intendedvolume rendering result may be obtained. The medical image datagenerator 120 of the medical image processing apparatus 10 according toan embodiment of the present invention may perform volume rendering andgenerate medical image data using the preceding method.

FIG. 9 is a block diagram of the medical image data generator 120according to an embodiment of the present invention. Referring to FIG.9, the medical image data generator 120 according to an embodiment ofthe present invention may include a HU setting unit 122 and a volumerenderer 124.

The volume renderer 124 receives the medical image of the object, andperforms volume rendering on the received medical image to generatemedical image data. As described above, the medical image may include atleast one of an X-ray image, a CT image, a PET image, an ultrasoundimage, and an MRI, but the present invention is not limited thereto.According to a further embodiment of the present invention, the volumerenderer 124 may perform volume rendering on the user defined auxiliarydata as well as the medical image of the object. The auxiliary data mayrepresent arbitrary information whose size and position are defined inreference to a medical image coordinate system such as a path, acritical zone, and the like previously prepared by the user.

In general, the auxiliary data may be defined in the form of a trianglemesh and drawn separately from the medical image and then synthesized.However, according to an exemplary embodiment of the present invention,the volume rendering may be performed after synthesizing previouslyprepared auxiliary data with the medical image. In order to perform thevolume rendering of the auxiliary data together with the medical image,the auxiliary data may be represented as voxels having a predeterminedrange of values.

In the case of CT, which is the most widely used medical image, the CTvalues of each component of the human body are shown in Table 1 below.In this case, the unit of each value is Hounsfield Unit (HU).

TABLE 1 Tissue CT Number (HU) Bone +1000 Liver 40~60 White matter−20~−30 Gray matter −37~−45 Blood 40 Muscle 10~40 Kidney 30Cerebrospinal Fluid (CSF) 15 Water 0 Fat −50~−100 Air −1000

Data according to digital imaging and communications in medicine(DICOM), which is the medical imaging standard, uses 2 bytes per pixel.Thus, the range of values each pixel can have is 2¹⁶, ranging from−32768 to 32767. Foreign substances such as implants may be insertedinto the human body, but they are substituted with appropriate valuesduring the reconstruction process so that values outside the range of+/−1000 HU are not used in the CT.

Therefore, according to an embodiment of the present invention, theauxiliary data may be represented as a voxel having a value outside thepre-defined HU range. In this case, the pre-defined HU range may be from−1000 HU to +1000 HU, but the present invention is not limited thereto.The HU setting unit 122 may substitute the voxel value corresponding tothe position occupied by the auxiliary data in the medical image datawith a value outside the range of +/−1000 HU. The volume renderer 124obtains the voxel data substituted by the value outside the pre-definedHU range from the HU setting unit 122 and performs volume rendering onit together with the medical image. When performing volume rendering ofthe auxiliary data together with the medical image, the amount ofcomputation required to render additional data included in the medicalimage may be minimized.

According to a further embodiment of the present invention, the rangeoutside the pre-defined HU range may include the first HU rangeexceeding the first threshold and the second HU range below the secondthreshold. In this case, the first threshold may be +1000 HU, and thesecond threshold may be −1000 HU. The HU setting unit 122 may set avalue of the first HU range and a value of the second HU range torepresent different types of auxiliary data. For example, the value ofthe first HU range may represent marker information set by the user, andthe value of the second HU range may represent path information.According to another embodiment, the value of the first HU range mayrepresent path information, and the value of the second HU range mayrepresent critical zone information. By representing the auxiliary dataas voxels having different ranges of values, the user may easilyidentify different types of auxiliary data. The above-mentionedclassification criteria of the auxiliary data type and the HU rangeallocation method are illustrative of the present invention, and thepresent invention is not limited thereto.

FIG. 10 is a block diagram of a medical image processing apparatus 20according to another embodiment of the present invention. Asillustrated, the medical image processing apparatus 20 according to anembodiment of the present invention includes a processor 21, acommunication unit 22, an input unit 23, a memory 24, a positiontracking unit 25, and a display output unit 26.

First, the communication unit 22 includes a wired/wireless communicationmodule of various protocols for communicating with an external device.The input unit 23 includes various types of interfaces for receiving auser input for the medical image processing apparatus 20. According toan embodiment, the input unit 23 may include a keyboard, a mouse, acamera, a microphone, a pointer, a USB, a connection port with anexternal device, and the like, but the present invention is not limitedthereto. The medical image processing apparatus may obtain a medicalimage of the object through the communication unit 22 and/or the inputunit 23 in advance. The memory 24 stores a control program used in themedical image processing apparatus 10 and various data related thereto.For example, the memory 24 may store a previously obtained medical imageof an object. In addition, the memory 24 may store medical image datagenerated by rendering a medical image of the object.

The position tracking unit 25 obtains position information of themedical navigation device 55 in the object. In the embodiment of thepresent invention, the medical navigation device 55 may include variouskinds of surgical navigation devices. An optical position trackingmethod or an electromagnetic position tracking method may be used forposition tracking of a medical navigation device, but the presentinvention is not limited thereto. If the position information obtainedfrom the medical navigation device 55 is not matched with the medicalimage data of the object, the position tracking unit 25 may perform amatching process to generate position information of the medicalnavigation device 55 in reference to the medical image data. Theposition tracking unit 25 may be connected to the medical navigationdevice 55 by wire or wireless to receive position information from themedical navigation device 55.

The display output unit 26 outputs an image generated according to anembodiment of the present invention. That is, the display output unit 26may output medical image data corresponding to the region of interestwith respect to the object as described below. The image output by thedisplay output unit 26 may be displayed by the monitor 65 connected tothe medical image processing apparatus 20.

The processor 21 of the present invention may execute various commandsor programs and process data in the medical image processing apparatus20. In addition, the processor 21 may control each unit of the precedingmedical image processing apparatus 20 and control data transmission andreception between the units.

The medical image processing apparatus 20 illustrated in FIG. 10 is ablock diagram according to an exemplary embodiment of the presentinvention, in which the separately displayed blocks logicallydistinguish elements of the apparatus. Therefore, the preceding elementsof the medical image processing apparatus 20 may be mounted on one chipor on plural chips according to the design of the correspondingapparatus. In addition, some of the components of the medical imageprocessing apparatus 20 illustrated in FIG. 10 may be omitted, andadditional components may be included in the medical image processingapparatus 20.

FIG. 11 is a more detailed block diagram of a processor 21 of themedical image processing apparatus 20 according to another embodiment ofthe present invention. As illustrated, the processor 21 of the medicalimage processing apparatus 20 according to another embodiment of thepresent invention may include a region of interest (ROI) setting unit210, a medical image data generator 220, and a partial medical imagedata generator 230.

The ROI setting unit 210 sets the ROI of the user with respect to theobject. More specifically, the ROI setting unit 210 receives theposition information of the medical navigation device 55 from theposition tracking unit 25 and sets the ROI based on the positioninformation. According to an embodiment of the present invention, theROI is set based on an area within a preset distance from the positionof the medical navigation device 55 in reference to at least one of thehorizontal plane, the sagittal plane, and the coronal plane of themedical image data. As such, the ROI may be set as a three-dimensionalregion including an area within a preset distance from a plane based onthe position of the medical navigation device 55. Therefore, the ROI maybe set as a slab having a thickness based on the preset distance.According to an embodiment, the ROI may be set in reference to at leastone of the horizontal plane, the sagittal plane, and the coronal planeof the medical image data. To this end, the ROI setting unit 210 mayreceive in advance, as a user input, information on a preset distance(i.e., area setting information) in reference to each of the horizontalplane, the sagittal plane, and the coronal plane. The ROI setting unit210 sets an ROI by cropping an area included, from the position of themedical navigation device 55, within the first distance in reference tothe horizontal plane, within the second distance in reference to thesagittal plane, and/or within the third distance in reference to thecoronal plane. If the user does not input area setting information on atleast one reference plane among the horizontal plane, the sagittal planeand the coronal plane, the ROI setting unit 210 may not perform croppingin reference to the plane. The ROI information obtained by the ROIsetting unit 210 is transferred to the partial medical image datagenerator 230.

Next, the medical image data generator 220 renders a medical image ofthe object to generate medical image data. As described above, themedical image includes at least one of an X-ray image, a CT image, a PETimage, an ultrasound image, and an MRI. The medical image data may referto voxels generated using the medical image of the object. However, thepresent invention is not limited thereto, and the medical image data mayrefer to data obtained by volume rendering the medical image of anobject.

Next, the partial medical image data generator 230 extracts and rendersmedical image data of a portion corresponding to the ROI among themedical image data of the object. More specifically, the partial medicalimage data generator 230 may perform volume rendering by selectively raycasting voxels of the ROI. Accordingly, by preventing objects other thanthe ROI from overlapping with objects of the ROI within the object, theoperator can easily identify the anatomical structure of the object.

According to an embodiment of the present invention, the partial medicalimage data generator 230 may generate volume rendering data in variousways. According to an embodiment, the partial medical image datagenerator 230 may generate volume rendering data by performing raycasting on all of the voxels included in the ROI.

According to another embodiment of the present invention, the partialmedical image data generator 230 may generate volume rendering data byselectively performing ray casting on voxels having a value within apre-defined HU range in the ROI. In this case, the pre-defined HU rangemay be determined based on the CT value of a specific tissue of theobject. In addition, the specific tissue for performing the volumerendering may be selected by the user. In this way, volume renderingdata may be generated by selectively performing ray casting only onvoxels corresponding to a specific tissue selected by a user setting inthe ROI.

As explained through Table 1, the range of CT values of each componentof a human body is predetermined. If the user wants to selectively checkonly gray matter in the ROI with respect to the object, the user mayinput an arbitrary value within the CT value range of −37 to −45 orinput a CT value range including the corresponding range through theinput unit 23. In addition, the user may input a selection for graymatter among predetermined tissues of the object through the input unit23. The partial medical image data generator 230 may generate volumerendering data by selectively performing ray casting only on voxelscorresponding to the gray matter within the ROI of the object based onthe user input.

According to another exemplary embodiment of the present invention, thepartial medical image data generator 230 may generate partial medicalimage data by rendering voxel values of an ROI when light is emittedfrom a virtual light source at a predetermined point based on theposition of the medical navigation device 55. More specifically, thepartial medical image data generator 230 may assume that a virtual lightsource exists at a predetermined point based on the position of themedical navigation device 55, and set voxel values of an ROI when lightis emitted from the virtual light source. The partial medical image datagenerator 230 may generate volume rendering data by performing raycasting on the voxels set as described above. Specific embodimentsthereof will be described later.

The partial medical image data generated by the partial medical imagedata generator 230 may be provided as an output image of the displayoutput unit 26.

FIG. 12 illustrates an example of defining an ROI with respect to anobject. Referring to FIG. 12, in the color cube for performing thevolume rendering, an area included within a specific distance inreference to the sagittal plane is set as the ROI. FIG. 13 illustratespartial medical image data corresponding to the ROI defined as describedabove. More specifically, FIG. 13(a) illustrates volume rendering dataof an object included in a cube, and FIG. 13(b) illustrates volumerendering data corresponding to the ROI defined in an embodiment of FIG.12. As shown in FIG. 13(b), according to the ROI setting of the user,only an area included within a specific distance in reference to thesagittal plane of the object may be volume-rendered and displayed.

FIG. 14 illustrates an embodiment of a user interface for defining anROI of an object. Referring to FIG. 14, the user interface may receiveinformation (i.e., area setting information) on a preset distance inreference to each of the horizontal plane, the sagittal plane, and thecoronal plane of the object from the user. The ROI is set based on anarea within a preset distance from the position of the medicalnavigation device 55 in reference to at least one of the horizontalplane, the sagittal plane, and the coronal plane of the medical imagedata. According to an embodiment of the present invention, the positioninformation of the medical navigation device 55 obtained from theposition tracking unit 25 may be displayed in a specific coordinate onthe slide bar for each reference plane in the user interface. The usermay set a reference distance to be included in the ROI based on thecoordinates displayed on each slide bar. The ROI setting unit 210receives at least one of first distance information in reference to thehorizontal plane, second distance information in reference to thesagittal plane, and third distance information in reference to thecoronal plane through the user interface. The ROI setting unit 210 setsan ROI by cropping an area included, from the position of the medicalnavigation device 55, within the first distance in reference to thehorizontal plane, within the second distance in reference to thesagittal plane, and/or within the third distance in reference to thecoronal plane.

FIGS. 15 and 16 illustrate partial medical image data corresponding tovarious regions of interest. FIG. 15(a) illustrates a case where the ROIis set based on the sagittal plane of the object, FIG. 15(b) illustratesa case where the ROI is set based on the horizontal plane of the object,and FIG. 15(c) illustrates a case where the ROI is set based on thecoronal plane of the object, respectively. In addition, FIG. 16illustrates a case where the ROI is set based on all of the sagittalplane, the horizontal plane, and the coronal plane of the object. Asdescribed above, according to the embodiment of the present invention,the ROI may be set in various forms according to the user setting, andonly the medical image corresponding to the ROI may be selectivelyrendered and provided to the user.

Meanwhile, in the above embodiments, it is illustrated that the ROI isset based on the horizontal plane, sagittal plane, and coronal plane ofthe medical image data, but the present invention is not limitedthereto. In the present invention, the ROI may be set with respect toany reference axis or reference plane of the medical image data.

FIG. 17 illustrates a method of generating partial medical image dataaccording to an additional embodiment of the present invention. Asdescribed above, the partial medical image data generator 230 maygenerate the partial medical image data by rendering voxel values of theROI under an assumption that light is emitted from a virtual lightsource at a predetermined point for a special effect on the ROI 30.

First, each pixel value I(S₀,S_(n)) of the volume rendering data usingthe general ray casting method may be expressed by Equation 1 below.

$\begin{matrix}{{I( {S_{0},S_{n}} )} = {\int_{S_{0}}^{S_{n}}{\{ {{{I_{\lambda}(x)}e^{- {\int_{S_{0}}^{x}{{\tau{(t)}}dt}}}} + {K_{ref} \cdot L \cdot e^{- {\int_{P_{0}}^{x}{{\tau{(t)}}{dt}}}}}} \}{dx}}}} & \lbrack {{Equation}\mspace{14mu} 1} \rbrack\end{matrix}$

Here, S₀ denotes the first voxel sampled by ray casting, and S_(n)denotes the last voxel sampled by ray casting. In addition, I_(λ)(x)denotes a value of the voxel x (or an intensity of the voxel x), ande^(−∫s) ⁰ ^(x) ^(τ(t)dt) denotes a transparency accumulated from thefirst voxel S₀ to the current voxel x. τ (t) denotes an attenuationcoefficient of the voxel t.

According to an embodiment of the present invention, it is assumed thata virtual light source exists at a predetermined point P₀ based on theposition of the medical navigation device 55, and the voxel values ofthe ROI 30 may be set when the light is emitted from the virtual lightsource. In this case, the value I′_(λ)(x) of the voxel x may beexpressed by Equation 2 below.I′ _(λ)(x)=I _(λ)(x)R(x)  [Equation 2]

Here, R(x) is a voxel value adjusted by the light emitted from thevirtual light source and may be defined as in Equation 3 below.R(x)=K _(ref) ·L·e ^(−∫P) ⁰ ^(x) ^(τ(t)dt)  [Equation 3]

Here, K_(ref) denotes a reflection coefficient, P₀ denotes a position ofthe virtual light source, and L denotes a brightness value of thevirtual light source at P₀, respectively. According to an embodiment ofthe present invention, the reflection coefficient K_(ref) may bedetermined as in Equation 4 below.K _(ref)=max(G(x)*V _(p0→x),0)  [Equation 4]

Here, G(x) denotes a gradient vector in the voxel x, and V_(p0→x)denotes the direction vector from the position P0 of the virtual lightsource to the voxel x, respectively. According to an embodiment, thegradient vector G(x) may be defined as a normal to a reference plane inwhich peripheral voxel values change most with respect to the voxel x.

Therefore, according to an embodiment of the present invention, eachpixel value I(S₀,S_(n)) of the partial medical image data may bedetermined based on Equation 5 below.

$\begin{matrix}{{I( {S_{0},S_{n}} )} = {\int_{S_{0}}^{S_{n}}{\{ {{{I_{\lambda}(x)}e^{- {\int_{S_{0}}^{x}{{\tau{(t)}}dt}}}} + {K_{ref} \cdot L \cdot e^{- {\int_{P_{0}}^{x}{{\tau{(t)}}{dt}}}}}} \}{dx}}}} & \lbrack {{Equation}\mspace{14mu} 5} \rbrack\end{matrix}$

The partial medical image data generator 230 sets the volume renderingdata generated as above as the partial medical image data. According tosuch an additional embodiment of the present invention, the effect maybe as if an illumination is inserted into or around the ROI. When anillumination is inserted into or around the ROI, the stereoscopic effectof the ROI may be maximized due to the shadow effect on the ROI, and theuser's identification of the ROI may be increased.

The description of the present invention is used for exemplification andthose skilled in the art will be able to understand that the presentinvention can be easily modified to other detailed forms withoutchanging the technical idea or an essential feature thereof. Thus, it isto be appreciated that the embodiments described above are intended tobe illustrative in every sense, and not restrictive. For example, eachcomponent described as a single type may be implemented to bedistributed and similarly, components described to be distributed mayalso be implemented in an associated form.

The scope of the present invention is represented by the claims to bedescribed below rather than the detailed description, and it is to beinterpreted that the meaning and scope of the claims and all the changesor modified forms derived from the equivalents thereof come within thescope of the present invention.

The invention claimed is:
 1. A medical image processing apparatus for amedical navigation device, comprising: a position tracking unitconfigured to obtain position information of the medical navigationdevice within an object; a memory configured to store medical image datagenerated based on a medical image of the object; and a processorconfigured to set a region of interest (ROI) based on positioninformation of the medical navigation device in reference to the medicalimage data, and generate partial medical image data corresponding to theROI, wherein the partial medical image data is generated by renderingvoxels in the ROI with a light from a virtual light source at apredetermined point based on a position of the medical navigationdevice, and wherein each pixel value I(S₀,S_(n)) of the partial medicalimage data is determined based on the following equation:I(S₀, S_(n)) = ∫_(S₀)^(S_(n)){I_(λ)(x)e^(−∫_(S₀)^(x)τ(t)dt) + K_(ref) ⋅ L ⋅ e^(−∫_(P₀)^(x)τ(t)dt)}dxherein S₀ is a first voxel sampled by ray casting S_(n) is a last voxelsampled by ray casting, Iλ(x) is a value of voxel x, τ(t) is anattenuation coefficient of voxel t, K_(ref) is a reflection coefficient,P₀ is a position of the virtual light source, L is a brightness value ofthe virtual light source at P₀.
 2. The apparatus of claim 1, wherein theROI is set based on an area within a preset distance from a position ofthe medical navigation device in reference to at least one of ahorizontal plane, a sagittal plane, and a coronal plane of the medicalimage data.
 3. The apparatus of claim 2, wherein the preset distance inreference to each of the horizontal plane, the sagittal plane, and thecoronal plane is determined by a user input.
 4. The apparatus of claim1, wherein the partial medical image data is generated by renderingvoxels in the ROI having a value within a pre-defined Hounsfield Unit(HU) range.
 5. The apparatus of claim 4, wherein the pre-defined HUrange is determined based on a CT value of a specific tissue of theobject.
 6. The apparatus of claim 5, wherein the specific tissue isdetermined by a selection of a user.
 7. The apparatus of claim 1,wherein the K_(ref) is determined based on the following equation,K _(ref)=max(G(x)*V _(p0→x),0) Herein, G (x) is a gradient vector atvoxel x, and V_(p0→x) is a direction vector from a position P₀ of thevirtual light source to voxel x.
 8. The apparatus of claim 1, whereinthe medical image data is set of voxels generated using the medicalimage of the object, and the partial medical image data is volumerendering data obtained by applying ray casting on voxels in the ROI. 9.A medical image processing method for a medical navigation device,comprising: obtaining position information of the medical navigationdevice within an object; storing medical image data generated based on amedical image of the object; setting a region of interest (ROI) based onposition information of the medical navigation device in reference tothe medical image data; and generating partial medical image datacorresponding to the ROI, wherein the partial medical image data isgenerated by rendering voxels in the ROI with a light from a virtuallight source at a predetermined point based on a position of the medicalnavigation device, and wherein each pixel value I(S₀,S_(n)) of thepartial medical image data is determined based on the followingequation:I(S₀, S_(n)) = ∫_(S₀)^(S_(n)){I_(λ)(x)e^(−∫_(S₀)^(x)τ(t)dt) + K_(ref) ⋅ L ⋅ e^(−∫_(P₀)^(x)τ(t)dt)}dxherein, S₀ is a first voxel sampled by ray casting, S_(n), is a lastvoxel sampled by ray casting, Iλ(x) is a value of voxel x, τ(t) is anattenuation coefficient of voxel t, K_(ref) is a reflection coefficient,P₀ is a position of the virtual light source, L is a brightness value ofthe virtual light source at P₀.
 10. The method of claim 9, wherein theROI is set based on an area within a preset distance from a position ofthe medical navigation device in reference to at least one of ahorizontal plane, a sagittal plane, and a coronal plane of the medicalimage data.
 11. The method of claim 10, wherein the preset distance inreference to each of the horizontal plane, the sagittal plane, and thecoronal plane is determined by a user input.
 12. The method of claim 9,wherein the partial medical image data is generated by rendering voxelsin the ROI having a value within a pre-defined Hounsfield Unit (HU)range.
 13. The method of claim 12, wherein the pre-defined HU range isdetermined based on a CT value of a specific tissue of the object. 14.The method of claim 13, wherein the specific tissue is determined by aselection of a user.
 15. The method of claim 9, wherein the K_(ref) isdetermined based on the following equation,K _(ref)=max(G(x)*V _(p0→x),0) Herein, G (x) is a gradient vector atvoxel x, and V_(p0→x) is a direction vector from a position P₀ of thevirtual light source to voxel x.
 16. The method of claim 9, wherein themedical image data is set of voxels generated using the medical image ofthe object, and the partial medical image data is volume rendering dataobtained by applying ray casting on voxels in the ROI.